In a vehicle drivetrain, a torque converter is situated between an engine and an automatic transmission. The automatic transmission may be in the form of a continuously variable transmission (CVT). A lock-up clutch is included in the torque converter to interconnect an input element and an output element of the torque converter. A lock-up control arrangement includes a lock-up control valve and a lock-up solenoid whose duty is variable under the control of a transmission controller.
At rapid deceleration, it is needed to release the engagement of the lock-up clutch well before the engine stalls. The transmission controller generates a lock-up release command and the lock-up control arrangement triggers movement of the lock-up control valve to a lock-up release position in response to the lock-up command.
JP-A 4-370465 teaches releasing the lock-up clutch in response to deceleration, which the transmission output shaft is subject to at rapid deceleration. When the magnitude of deceleration becomes greater than a predetermined reference, the transmission controller generates a lock-up release command.
An object of the present invention is to provide a lock-up control system for a vehicle drivetrain, which can generate a lock-up release command at deceleration with any magnitude of deceleration out of a range over all of available magnitudes of deceleration.